Waste acids containing Fe, Ni and SO4 are generated when metal components (nickel (Ni), iron (Fe)) are treated with sulfuric acid in the method of manufacturing diamond.
In general, the liquid waste generated in the method of manufacturing diamond includes 1 to 2% of Ni, 3 to 6% of Fe, and 30 to 40% of SO4.
When Fe and Ni are present in the liquid phase, there is proposed a method of separating Fe and Ni in the form of FeOOH and NiO and recovering the Fe and Ni as an alternative to recycle Ni (Korean Patent Application No. 1998-56697, Registered Patent No. 0406367)
The above-mentioned method of recycling an Fe/Ni sludge will be described in detail, as follows.
That is to say, an iron chloride (FeCl2)/nickel chloride (NiCl2)-containing aqueous solution is prepared by dissolving an Fe/Ni-containing sludge in hydrochloric acid so that the aqueous solution can be adjusted to pH 3 to 4, and FeCl2 is oxidized into FeCl3 by blowing air or hydrogen into the chlorides-containing aqueous solution.
Next, the generated FeCl3 reacts in water at pH 3 to 5 to form an orange iron hydroxide (FeOOH) core, and an iron hydroxide sludge is formed by adding alkali to the iron hydroxide (FeOOH) core under the oxidation atmosphere so that the solution can be maintained up to twice mole of Fe in the solution, and to pH 3 to 5.
Then, the formed iron hydroxide sludge is filtered to separate an NiCl2-containing filtrate from the iron hydroxide sludge, and the iron hydroxide sludge is then washed to obtain an iron hydroxide.
Finally, a nickel hydroxide precipitate is formed by adding alkali to the separated filtrate so that the filtrate can be maintained to pH 10 or more, and the nickel hydroxide precipitate is filtered, and washed to obtain nickel hydroxide.
However, the method of recovering and recycling iron hydroxide and nickel hydroxide as described above may apply only to chlorides.
That is to say, Fe and Ni are relatively easily separated from an FeCl2/NiCl2 aqueous solution, but when slaked lime as alkali is added to an SO4-rich solution, a large amount of Ni is lost in the process of removal of Fe, which leads to the very low Ni recovery rate in the manufacture of nickel hydroxide.
In order to employ the Fe/Ni-containing material which is obtained from the liquid waste as a raw material of stainless steel, the Fe/Ni-containing sludge is also subject to the drying and sintering processes, but the Fe/Ni-containing sludge may be degraded in these processes.
Therefore, in order to employ the Fe/Ni-containing material as the stainless steel material, it is necessary to agglomerate the Fe/Ni-containing material into a pellet and the like.
In order to realize a desired strength of an agglomerated mass for raw material of stainless steel according to the solidification method using powder of the Fe/Ni-containing material prepared according to the above-mentioned method, the Fe/Ni-containing material is milled into powder, and the powder may be agglomerated by adding an agglomerant additive to the powder of the Fe/Ni-containing material, and mixing and molding them.
However, the initial moisture content and the initial curing strength of the pellet are highly varied according to the resulting Fe/Ni-containing sludge.
In particular, when an FeNi sludge in an aqueous solution is formed through the wet reaction, the problem is that a short-term curing moisture content of the FeNi sludge is high and a short-term curing strength of the FeNi sludge is very low in the agglomeration (pelletizing) process.
Therefore, the curing time may be extended long when a mass, for example a pellet, for a stainless steel material is manufactured using the Ni-containing wet sludge as the stainless steel material.